1. Field of the Invention
The present invention relates in general to power supply circuits and DC/DC converters, and is particularly directed to delaying enabling and disabling of diode-emulation in a DC/DC converter, including converters used to supply power to microprocessors, in such a manner as to prevent potential damage caused by output voltage bumps.
2. Description of the Related Art
When the load current of a DC/DC converter is very low, operating the converter in a mode called “diode emulation” leads to less power wasted by the converter. During diode emulation, the current in the power inductor is prevented from flowing in the reverse direction (that is, flowing from the output back to the input). When the converter is not performing diode emulation, the inductor current may flow in either direction. Thus, as diode emulation is enabled or disabled, the waveform of the current through the inductor changes. While the change is occurring, the inductor current may have a momentary change in its average current. For the brief moment that the average current is different, the DC/DC converter is not supplying the current demanded by the load. To compensate for the change in current from the inductor, the output capacitor supplies current, which causes the capacitor voltage to change. Since the capacitor voltage is also the output voltage of the converter, the output voltage changes. In particular, the output voltage of the DC/DC converter “bumps” up when diode emulation is enabled and bumps down when diode emulation is disabled.
The output voltage bumps generated when diode emulation is enabled or disabled may cause a malfunction of logic circuits being powered by the converter. One solution has been to simply disable diode emulation when providing power to circuitry that may be damaged by the voltage bumps, such as microprocessors or the like. Yet the disablement solution obviously eliminates the benefits associated with diode emulation including power savings, which is particularly advantageous for microprocessor circuits. It is desired, therefore, to enable and disable the diode emulation mode of operation while eliminating any potential damage to the logic circuits being powered by the DC/DC converter.